CanEver Audio ZeroUno D/A processor

It's the sad realization at the heart of every product review: No matter what the writer has to say, the reader may hear thingsor see or feel or taste thingsrather differently. I refer not only to physiological differences in hearing acuity from person to person, but also to the no-less-critical differences in the ways we process and prioritize the things we perceive. It's an oft-made point that bears any amount of repetition: In our pugilistic little pastime, the priorities of the listener who values, say, fidelity to the musical timing captured in a recording over fidelity to that recording's timbral truths are no less legitimate than those of the enthusiast whose priorities are the other way around. Both approachesand any number of othersbend toward the sun of high fidelity.

A case in point is the ZeroUno DAC ($7990), the first product from CanEver Audio, an Italian firm. By the end of its stay in my home, it had pushed virtually all of my Happy buttonsnot by doing everything I could ask of it, but by having a point of view that aligned with my own. But even now, as I praise its sound quality and its apparently reasonable level of value for the money, I'm less sure than usual whether I liked this product because it agreed with me or because it was right. But I'm getting ahead of myself . . .

Description
The single-box CanEver ZeroUno breaks convention by looking more like a low-power tubed amplifier than a DAC: the top of its steel enclosure, which measures 15.5" wide by 13.5" deep, is occupied by two Psvane CV181 dual-triode vacuum tubes and three soup-cansized cylinders that bring the ZeroUno's overall height to 8". It isn't hard to imagine a mains transformer and a stereo pair of output transformers inside those cylinders, but the reality is slightly different. The cylinders at the sides contain toroidal transformers: the one on the left for the tubes' heater filaments, the one on the right for the digital circuitry. Inside the central can are two toroidal transformers: one for the two tubes' output stages, the other for the DAC's analog circuitry.

The front panel is attractively simple. Flanking an LCD display screen are two 1.5"-diameter knobs: on the left a rotary power switch, on the right a knob that addresses a 32-bit internal volume control. Also on the front are two pushbuttons: Input selects between the ZeroUno's four inputsUSB, S/PDIF BNC, S/PDIF RCA, and S/PDIF opticaland Setup's jobs I'll describe in the next section. Around back are one pair each of RCA and XLR output jacks, both carrying a single-ended signal, and jacks for the four inputs listed above. CanEver says that an AES/EBU jack can be substituted for the BNC input jack, if desired.

As for the CV181s, which are equivalents of the more commonly seen 6SN7 tube, designer Mario Canever told me in an e-mail that they're used "to match the signal transfer between the output stage of the ZeroUno DAC, the connecting signals cables, and the input values of the . . . amplifier." Voltage gain for the ZeroUno's output stage is provided by an interstage transformer before the tubeas Canever observes, "it works as a step up transformer"mounted on the substantial main circuit board.

At the heart of the ZeroUno is an ESS Sabre32 ES9018S chip, its eight internal differential DACs used in a quad-sum configuration. Apparently, considerable engineering effort went into the ZeroUno's digital and analog filtering. As Mario Canever explained, sigma-delta DACs such as the Sabre are often wrongly criticized for generating excessive noise: "This 'noise' is really the same useful signal you listen to with your ears, plus the same signal, but shifted in frequency. Knowing the exact nature of this 'noise,' it is simple to filter it." Canever's solution is to apply his own digital filter designsan infinite impulse response (IIR) filter for DSD and finite impulse response (FIR) filters for PCM, implemented in the Sabre chipplus his own stereo analog filter, placed between the Sabre and the ZeroUno's output stage. "Upgrades are possible," he added, "while making changes to [this] proprietary firmware."

The ZeroUno's USB input board, which is separate from its main circuit board, is designed around an XMOS chip, and offers a standard USB 2.0 interface. No additional drivers are required for use with Apple OS or Linux systems; driver-installation instructions are provided for Windows users. In late 2016, when my review sample was supplied, the ZeroUno was described as supporting, via its USB input, PCM up to 384kHz as well as DSD over PCM (DoP) up to DSD128. (Separate crystal-oscillator clocks are included for sampling rates of 44.1 and 48kHz and their multiples.) Canever says that the ZeroUno will soon be able to support MQA, by means of a retrofittable USB input board the company plans to introduce in May 2017, at the High End show in Munich.

Finally, a few words are due the ZeroUno's power-supply section, which reportedly benefits from a concentrated effort to achieve low noise and high independence of individual circuits. All those individual toroidal transformers noted above contribute to this independence. So, too, does the fact that the USB receiver board is given a high degree of electrical isolation from just about everything else, given that it's powered not by the lousy 5V on the USB bus, but by a "quasi-battery" power supply. Overall, the ZeroUno's power supply is claimed to contain 13 individual coupling inductors, and is built using "aluminum organic solid polymer" capacitors instead of electrolytic types.

Installation and Setup
Usually, there's not much to say about setting up a new USB DAC with an Apple iMac: You connect the two with a USB link (I used a 2m AudioQuest Carbon), select the new output device in the iMac's System Preferences window, and, if necessary, dink around with the settings of your music-playback software until everything works.

This time, things were different, given that I'd recently switched to the Roon music-playback app (v.1.2, Build 165), having been inspired by Jon Iverson's and Michael Lavorgna's very positive reports on same. While this is neither the time nor the place to kill several hundred innocent words in an attempt to describe my experiences with it, I'm impressed with Roon's metadata-intensive and generally (but not consistently) high-level interface, while I consider its sound to be at least as good as that of Audirvana and Decibel, my previous favorite players.

It turned out that Roon is also amenable to changes in hardwareso amenable that my efforts at futzing around with my iMac's Audio MIDI Setup screen only made things worse. Michael Lavorgna advised me to simply let Roon sort things out, so I rebooted computer and DAC alike, then simply clicked on the appropriate audio-output devicelabeled xCORE USB Audio 2.0in the iMac's System Preferences window. From that point forward, all worked well: The ZeroUno DAC adapted, easily and instantly, to changes in file resolution, and its LCD screen correctly displayed all music-file sampling rates.

All told, the ZeroUno has ten user-adjustable functions: three affecting the brightness of the LCD display and the size of certain characters thereon, and seven affecting various aspects of performance. Some of the latter, such as adjusting channel Balance and inverting Phase (absolute signal polarity), are self-explanatory, but the purposes of the rest range from obscure to full-bore WTF, and none is explained in the owner's manual. These are: Oversampling Filter (On/Off, default On); Jitter Filter (On/Off, default On); FIR Filter, for USB only (Smooth/Sharp, default Smooth); IIR Filter, for DSD only (Maximum/Medium/Minimum, default setting not indicated); and DAC Resolution (6, 7, 8, or 9 bitsbut given the lack of explanation, the choices might as well be Goldfish, Hamster, Kitten, or Puppy).

I spent weeks listening to the ZeroUno in its default mode, and with its digital Volume control turned all the way up (ie, 0dB of attenuation). At first, the only one of the DAC's ergonomic and performance functions that interested me was the ability to play around with signal polarity. A repurposed Apple remote handset is supplied with the ZeroUno, and its Phase button is, wisely, the largest and most centrally located control on the whole blessed thing. So that's the only user control this user used . . . for a while.

Then something odd happened: In a moment of clumsiness, I accidentally disconnected the 2m USB link between the ZeroUno and my iMac, and when I reconnected it, my computer would no longer communicate with the DAC. The ZeroUno was still a selectable option in the iMac's System Preferences, again as xCORE USB Audio 2.0, but it would not remain selected.

So I hard-rebooted everything, including the CanEver ZeroUno, then reselected the ZeroUno in System Preferences. Now it stayed selectedbut the unit's display remained resolutely dark. Initiating the Setup procedureaccomplished by pressing the Setup button for more than 2 seconds but fewer than 10illuminated the screen at what I assume was its dimmest setting. Music played, it sounded fine, and I could still use the handset to invert signal polarity, as desired. But I soon realized that, while the manual instructs the user how to enter Setup mode, and how to cycle through the various settings within each function using the Volume knob, it offers not the slightest idea of how to move between functions; eg, Phase, Balance, Jitter Filter, etc.

Good Morning Art, thank you for the passion that you transmit while doing your job. I don't understand how come that a converter that you find as the most capable DAC of your experience (Canever review) ends up in the class B rating. Please let us know. Kind regards. Stefano